The acetylcholine receptor translates the binding of acetylcholine into the flow of ions across the cell membrane and thus serves a major role in the communication between nerve and muscle (or electrocyte). Of the diverse classes of pharmacological agents that interact with the acetylcholine receptor, the noncompetitive blockers have been shown to block responses to acetylcholine without interacting with the acetylcholine binding site. This has led to suggestions that these agents bind directly to the ion channel, although an allosteric mechanism is also possible. The studies proposed here, using the acetylcholine receptor from the electroplaque of electric fish, are designed to explore the mechanism of action of noncompetitive blockers. Studies have been designed to test using biochemical techniques whether these agents interact directly with the ion channel and to investigate further the allosteric coupling between the acetylcholine binding site and the site for noncompetitive blockers. Furthermore, a variety of structural studies are proposed to relate the structure and posttranslational modifications of the acetylcholine receptor to the functional regulation by noncompetitive blockers (using the techniques of photoaffinity labeling, proteolytic digestion and monoclonal antibodies). A technique for studying the binding of these agents to the soluble receptor will be used to extend these studies to skeletal muscle. In skeletal muscle, studies will be designed to understand the structural and functional differences between different varieties of receptors (e.g., junctional, extrajunctional, embryonic). Skeletal muscle acetylcholine receptors are of considerable interest due to their potential role in the stable formation of contacts between nerve and muscle cells and their role as the major autoantigen in myasthenia gravis. In addition these studies will be of general interest to the understanding of neuromuscular disease in which an ionophoric defect may be involved (e.g., myotonic muscular dystrophy) and of denervation neuromuscular diseases (e.g., amyotrophic lateral sclerosis and peripheral neuropathy).